450 BACTERIOLOGICAL ANALYSES 



mass, which can be shown to contain some organisms 

 and a few leucocytes. 



(b) A central layer of separated milk, thin, watery, 

 and opalescent, and containing extremely few bacteria. 



(c) A sediment or deposit consisting of the great 

 majority of the contained bacteria and leucocytes, 

 together with adventitious matter, such as dirt, hair, 

 epithelial cells, faecal debris, etc. 



5. Withdraw the rubber stopper and remove a 

 central plug of cream from each tube by means of a 

 sterile cork borer ; place these masses of cream in two 

 sterile capsules. Label C 1 and C 2 . 



6. Remove all but the last one or two c.c. of separated 

 milk from each tube, by means of sterile pipettes. 



7. Mix the deposits thoroughly with the residual 

 milk, pipette the mixture from each pair of tubes into 

 one sterile 10 c.c. tube (graduated) by means of sterile 

 teat pipettes, then fill to the 10 c.c. mark with sterile 

 normal saline solution and mix together. Label D 1 and 

 D 2 . 



8. Place the two tubes of mixed deposit in the 

 centrifuge, adjust by the addition or subtraction of 

 saline solution so that they counterpoise exactly, and 

 centrifugalise for ten minutes. 



NOTE. Each tube now contains the deposit from 100 c.c. of 

 the milk sample and the amount can be read off in hundredths 

 of a centimetre. The multiplication of this figure by 100 will 

 give the amount of "Apparent Filth," in "parts per million" the 

 usual method of recording this quality of milk. 



9. Pipette off all the supernatant fluid and invert the 

 tube to drain on to a pad of sterilised cotton-wool, 

 contained in a beaker. (This wool is subsequently 

 cremated.) 



10. Examine both cream (C 1 ) and deposit (D 1 ) 

 microscopically 



(a) In hanging-drop preparations. 



(b) In film preparations stained carbolic methylene- 



